1. Field of the Invention
The present invention relates to a vehicle stabilizer bushing entirely made of rubber having a sliding surface on the inner side thereof particularly suitable for mounting a stabilizer bar in automobile suspension on the vehicle body or suspension. The present invention can be applied also to a rubber laminate having a sliding rubber portion other than stabilizer bushing.
The present application is based on Japanese Patent Applications No. 2000-73651 and No. 2000-215001, which are incorporated herein by reference.
2. Description of the Related Art
A conventional vehicle stabilizer bushing 112 has a structure as shown in FIG. 10 (see JP-A-60-180619 (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d)).
A rubber elastic member 10 constituting the stabilizer bushing 112 is essentially a cylindrical material surrounded by an inner surface 114 and an outer surface 16 (formed by a U-shaped surface 16a and a flat surface 16b closing the upper opening thereof). The cylindrical material is provided with a flange portion 101 at the both axial ends of the U-shaped surface 16a and a cut 120 for allowing a stabilizer bar S to be inserted thereinto. The vehicle stabilizer bar S is inserted into and retained by the thick cylindrical rubber elastic member 10.
In order to mount the bushing 112 on the vehicle body, the bushing 112 is fitted on the stabilizer bar S through the cut 120, and then mounted on the vehicle body with a bracket 20. In some detail, the both mounting seats 20b of the U-shaped retaining portion are screwed to the vehicle body (not shown) through a hole 201 with the U-shaped surface of the bushing 112 being retained by the bracket 20 at its U-shaped retaining portion 20a. 
The radially protruding flange 101 provided at both axial ends of the rubber elastic member 10 prevents the rubber elastic member 10 from coming off from the bracket 20.
It has been found that when the torsional torque developed upon the reception of torsion of the stabilizer bar S retained by the bushing 12 is reduced, it has an effect on the riding comfort. A known technique for reducing torsional torque of the stabilizer bar S is a bushing having an inner surface formed by a resin layer having high sliding properties (low friction coefficient) (JP-A-63-57310, JP-A-63-57311, etc.).
However, the bushing having an inner surface formed by a resin layer is disadvantageous in that the elastic modulus (spring constant) of the entire bushing can hardly be lowered than a predetermined value since the resin material has a high elastic modulus (spring constant) than the rubber material. On the other hand, in the case a soft rubber material is used as the rubber portion of the bushing so as to derive an elastic modulus (spring constant) of the entire bushing lower than a predetermined value, the resulting bushing has a deteriorated durability.
In order to cope with the foregoing problems, JP-A-10-82441 proposes a bushing 112a arranged such that a sliding rubber portion (rubber with high sliding properties) 10a which comes in contact with the stabilizer bar S is formed on the inner surface of a main body rubber portion (base rubber) 10b constituting the outer surface as shown in FIG. 12.
Further, a stabilizer bushing comprising a rubber elastic member 10 consisting of two layers, namely, inner layer rubber 10a made of a rubber material having high sliding properties and outer layer rubber 10b as shown in FIG. 11 has recently been studied. The structure of stabilizer bushing shown in FIG. 10 is disadvantageous in that the desired stability in operation and riding comfort can hardly be attained at the same time, that is, when the rigidity of the rubber elastic member 10 is raised to enhance the stability in operation, the riding comfort is deteriorated while when the rubber elastic member 10 is made of a softer material, the stability in operation is deteriorated. Meanwhile, the structure of FIG. 11 is advantageous in that the riding comfort is raised since the sliding resistance of the inner layer rubber 10a is low, as well as in that the stability in operation is improved since the outer layer rubber 10b can be made of a rubber material having a higher rigidity than that of the inner layer rubber 10a to enhance the rigidity of the rubber elastic member 10. Further, the generation of abnormal noise due to rapid relative displacement between the inner layer rubber 10a and the stabilizer bar S can be prevented.
However, the most modern design of vehicles requires that components be received in as small area as possible. Thus, there is no sufficient space between the components. Therefore, when the stabilizer bar S makes an axial relative movement with respect to the rubber elastic member 10 to show a horizontal shift, the stabilizer bar S can interfere with its surrounding components. In order to cope with this problem, a horizontal shift stopper 2 made of metal ring is provided around the stabilizer bar S as shown in FIG. 11 to control the relative movement. However, a new problem has arisen that the horizontal shift stopper 2 and the rubber elastic member 10 generate abnormal noise by an interference with each other.
Besides, the bushing 112a having the foregoing structure is normally prepared by using an injection mold as shown in FIG. 13.
In some detail, the main body rubber portion 10b is prepared by injection-molding a rubber material for main body rubber portion (first rubber compound) which has been injected through a first material injection passage 34 in a cavity for main body rubber portion 32 formed by a first top force 28 and a bottom force 30. When the vulcanization of the main body rubber portion 10b has proceeded to a certain extent, the first top force 28 is then replaced by a second top force 36. A rubber material for sliding rubber portion (second rubber compound) is then injected into a cavity for sliding rubber portion 38 formed inside the main body rubber portion 10b through a second material injection passage 40 so that it is injection-molded. When the vulcanization of the main body rubber portion 10b as well as the sliding rubber portion 10a has been completed, the mold is then opened to release the bushing (molded product)
It was found that if the vulcanization of the main body rubber portion 10b proceeds too much (e.g., 90% vulcanization) at the time the second rubber compound is injected, there cannot be made a sufficient vulcanized bonding (co-crosslinking: by simultaneous vulcanization) between the main body rubber portion 10b and the sliding rubber portion 10a. The term xe2x80x9cco-crosslinking (co-vulcanization)xe2x80x9d as used herein is meant to indicate crosslinking between different rubber phases. The term xe2x80x9cco-crosslinking agentxe2x80x9d as used herein is meant to indicate a vulcanizing agent to be added for the purpose of improving the foregoing xe2x80x9cco-crosslinkabilityxe2x80x9d.
If the time of injection of the second rubber compound is predetermined to be sooner from that of the first rubber compound (50% vulcanization), a sufficient vulcanized bonding strength can be attained. However, the main body rubber portion 10b is insufficiently vulcanized, reducing stability in shape of the main body rubber portion 10b. Thus, this approach is not practical. In other words, the injection pressure of the material for sliding rubber portion may cause the main body rubber portion 10b to be compressed or the raw material for sliding rubber portion to penetrate into interfaces between the main body rubber portion 10b and the forces 30, 36, generating defects in shape of the molded product.
It is an object of the present invention to provide a stabilizer bushing having a horizontal shift stopper provided thereon which can prevent the generation of abnormal noise due to the interference with the horizontal shift stopper without impairing the stability in operation or riding comfort.
It is another object of the present invention to provide a stabilizer bushing which allows vulcanized bonding of the sliding rubber portion to the main body rubber portion even if the sliding rubber portion material is injected when the vulcanization of the main body rubber portion is almost completed (90% or more vulcanization) and a process for the preparation thereof.
In accordance with the first aspect of the invention, a stabilizer bushing is provided comprising a stabilizer bar inserted in a cylindrically-formed rubber elastic member the outer surface of which is arranged to be retained by a bracket to be fixed to the vehicle body. Around the stabilizer bar is provided a stopper member for controlling the axial movement of the rubber elastic member. The rubber elastic member has a laminated structure comprising an inner layer rubber made of a rubber with-high sliding properties and an outer layer rubber laminated on the outer surface of the inner layer rubber. The rubber elastic member has a sliding surface made of a rubber with high sliding properties provided at least on the end face thereof facing the stopper member.
In accordance with the foregoing arrangement, the rubber elastic member has a sliding surface made of a rubber with high sliding properties and a reduced frictional resistance provided on the end face thereof facing the stopper member, making it possible to prevent the generation of abnormal noise even when the stabilizer bar makes horizontal shift to cause the rubber elastic member to interfere with the stopper member. Further, since the rubber elastic member has a laminated structure comprising a stabilizer bar-retaining inner layer made of a rubber with high sliding properties, the desired stability in operation and riding comfort can be attained at the same time, and the generation of abnormal noise due to interference with the stopper can be prevented, making it possible to realize a comfortable environment.
In accordance with the second aspect of the invention, the area of the sliding surface is predetermined to be equal to or more than that of the end face of the stopper member. In this arrangement, the outer layer rubber made of an ordinary rubber material and the stopper member can be prevented from interfering with each other, making it possible to prevent the generation of abnormal noise more securely.
In accordance with the third aspect of the invention, the sliding surface can be arranged to protrude beyond the end face of the outer layer rubber toward the stopper member. In this arrangement, too, the outer layer rubber and the stopper member can be prevented from interfering with each other, eliminating the necessity of making the area of the sliding surface greater than that of the stopper member and hence enhancing the degree of freedom of design.
In accordance with the fourth aspect of the invention, the sliding surface is provided integrally with the inner layer rubber. In this arrangement, the sliding surface can be molded integrally with the inner layer rubber during the molding of the inner layer rubber, making it easy to prepare the stabilizer bushing.
In accordance with the fifth aspect of the invention, the rubber elastic member comprises a pair of radially extending flange portions provided on the respective end face thereof, and the entire end faces of the rubber elastic member including the flange portion are made of a rubber with high sliding properties formed integrally with the inner layer rubber. In this arrangement, the outer layer rubber can be held interposed between the flange portions, making it possible to prevent the inner layer and the outer layer from shifting with respect to each other or coming off from each other.
In accordance with the sixth aspect of the invention, the hardness of the outer layer rubber is predetermined to be equal to or more than that of the inner layer rubber. By thus raising the hardness of the outer layer rubber, a necessary rigidity can be secured, making it possible to enhance the stability in operation.
In accordance with the seventh aspect of the invention, the external shape of the inner layer rubber is polygon or analogous to that of the outer layer rubber. In this arrangement, shift or rotation on the interface of the inner layer with the outer layer can be prevented, improving the adhesivity. The external shape of the inner layer rubber analogous to that of the outer layer is effective for the increase of the volume of the inner layer rubber.
In accordance with the eighth aspect of the invention, the foregoing objects can be accomplished with the following constitution.
A stabilizer bushing comprising a main body rubber portion formed of a sulfur-vulcanizable first rubber compound and a sliding rubber portion formed of a second rubber compound containing a sulfur-vulcanizable lubricant on the inner surface of the main body rubber portion, characterized in that the first rubber compound exhibits vulcanizability satisfying the following requirements:
t90t50
xe2x89xa71.5 min
and contains a crosslinking tackifier, t90 is a time to 90 vulcanization, t50 is a time to 50 vulcanization, and the vulcanizability is measured by a curastometer in accordance with JIS K 6300. In this arrangement, a sufficient adhesive strength of the sliding rubber portion with respect to the main body rubber portion can be secured even if the molding of the sliding rubber portion is effected after the passage of t90 of the main body rubber portion as shown in the testing examples described later.
The reason why the prolongation of (t90xe2x88x92t50) provides improvement of vulcanized adhesivity to vulcanized rubber is unknown. That is because it has been a common sense to those skilled in the art that the adhesivity strength of unvulcanized rubber with respect to vulcanized rubber of the same kind depends little on the vulcanization history of vulcanized rubber. Further, it is not known to those skilled in the art that the incorporation of an tackifier in a main body rubber portion causes a drastic increase of vulcanized adhesive strength (90xc2x0 peeling strength). In other words, an tackifier is inherently incorporated to improve the knead ability (adhesivity to roll) of rubber during kneading and the adhesivity of dough. The tackifier thus incorporated is mostly retained in the crosslinked structure (vulcanized network) and is a low molecular compound having low Tg (glass transition point). It was thus a common sense to those skilled in the art that an tackifier makes little contributions to the increase of vulcanized adhesive strength in an atmosphere of softening temperature (e.g., 80xc2x0 C. in the testing examples described later).
As the crosslinking tackifier there is preferably used a phenol-formaldehyde resin or phenol-polysulfide resin. Since a phenol-formaldehyde resin is used also as a crosslinking agent for diene-based rubber, it can be presumed that a phenol-formaldehyde resin acts as a co-crosslinking agent on the interface of the main body rubber portion with the sliding rubber portion. Further since the release of sulfur from a phenol-polysulfide resin is suppressed until shortly before the completion of vulcanization, it can be presumed that a phenol-polysulfide resin, too, acts as a co-crosslinking agent.
In the case where an NR-based rubber is used as a rubber polymer for the first rubber compound, an alkylphenol polysulfide (tackifier) is used as the phenol-polysulfide resin. The amount of the alkylphenol polysulfide to be incorporated is normally from 0.25 to 5 phr.
As the phenol to be used as a base there is used an alkylphenol from the standpoint of compatibility with NR-based rubber. When the amount of the tackifier to be incorporated is too small, the desired vulcanized adhesive strength of the sliding rubber portion with respect to the main body rubber portion after the passage of T90 can hardly be obtained. On the contrary, when the amount of the tackifier to be incorporated is too great, the vulcanized adhesive strength (rubber strength) is rather reduced and the permanent compression set of the rubber is adversely affected.
In the case where the rubber polymer to be used as the first rubber compound and second rubber compound in the foregoing various arrangements is an NR-based rubber, the vulcanization accelerator to be incorporated in the first rubber compound is normally a benzothiazole sulfide compound. This is because the use of such a vulcanization accelerator enables to control easily the vulcanization curve.
The constitution of the process for the preparation of the stabilizer bushing for vehicle of the invention is as follows.
A process for the preparation of a stabilizer bushing which comprises forming a main body rubber portion from a sulfur-vulcanizable first rubber compound, forming a sliding rubber portion from a sulfur-vulcanizable second rubber compound on the inner surface of the main body rubber portion, and then allowing the sliding rubber portion to be co-crosslinked to the main body rubber, characterized in that as the first rubber compound there is used one having vulcanizability satisfying the following requirements:
t90t50
xe2x89xa71.5 min
and containing a crosslinking tackifier, t90 is a time to 90% vulcanization, t50 is a time to 50% vulcanization, and the vulcanizability is measured by a curastometer in accordance with JIS K 6300.